Many biological, physical or chemical analysis methods are based on lipid bilayers and biological membranes, respectively. Some of these techniques require the direct access to specific parts/patches of the membrane being usually ca. 0.1-100 um (um=10−6 meter) in diameter. Examples are electrophysiological techniques such as Patch Clamp and Black Lipid Membrane (BLM) analysis. For the standard patch clamp, such parts/patches of the membrane have been exclusively accessed by sealing a micro pipette against the cell membrane. Access to the membrane patch beneath the pipette is then directly provided through this pipette. The remaining membrane area outside the pipette is usually accessed through the solution in which the cell is immersed (B. Sakmann and E. Neher, Ed., Single-Channel Recording, Plenum Pub. Corp.; ed. 1, 1983). In the case of artificial lipid membranes (e.g. BLM), thin and perforated insulating sheets separating two fluid compartments have been used to carry the membranes in such a way that they cover the hole and consequently can be independently accessed from both sides (Mueller et al., J. phys. Chem., 67, 534 (1963)).
Lately, micromachined planar solid substrates (also called ‘carrier’) made of sheets of insulating materials such as silicon/siliconnitride (PCT patent application WO1998IB0001150), glass and plastics have replaced the classical tools for directed membrane access such as micropipettes (as in patch clamp) and TEFLON® septa with conventional holes (as for BLM). Advantages include a much simplified handling during analysis, higher stability, better electrical parameters as well as the possibility to mass manufacture the new membrane carriers.
However, due to the specific needs of carriers for electrophysiology such as the surface adhesion properties and holes sizes as small as 0.1-10 um in ca. 2-200 um thick insulators, current standard materials as well as techniques used for micromachining may not provide a suitable approach to the production of inexpensive but high quality membrane carriers.
It has so far not been possible to produce high quality membrane carriers in a reproducible manner by dielectric breakdown phenomena. More specifically it has not been possible to reproducibly produce substrates having holes in them in which holes have a diameter in the range of 0.1 um to 10 um. It has also not been possible to introduce such holes in a manner allowing for mass production of such perforated substrates. Membrane carriers produced with other methods, such as e.g. lithography and other mainly for semiconductor industry developed micromachining technologies, usually lack one or more characteristics required for membrane carriers such as high aspect ratio holes (preferably >10), chemical and physical surface properties (e.g. functional groups on surface for modification; roughness), hole diameter and in particular simplicity and low cost of production.
Accordingly it was an object of the present invention to provide for a method allowing the production of high quality perforated substrates, e.g. of high quality membrane carriers. It was also an object of the present invention to provide for a method of production of such high quality membrane carriers which method is easy to perform and reproducible. It was furthermore an object to provide for a method allowing the controlled production of holes in substrates, wherein the geometrical features of the holes can be easily controlled and influenced. It was also an object of the present invention to provide for a method allowing the mass production of perforated substrates. It was furthermore an object of the present invention to provide a method of hole production that can be applied to substrates that were hitherto difficult to process, such as glass.